Quantitative RT-PCR for dengue serotyping is most useful in which phase of the illness relative to symptom onset?

• A Days 6–10 (defervescence/critical phase)
• B Days 1–5 of febrile illness (viraemic phase) ✓
• C Days 11–14 (recovery phase)
• D Any phase — viral load remains constant throughout illness

Explanation

Dengue viremia peaks in the first 3–5 days of febrile illness and then declines rapidly, with RNA typically undetectable by day 8–9. RT-PCR (NAAT) for dengue RNA/serotyping is therefore highly sensitive and appropriate during the early viraemic phase (days 1–5). After day 5, NS1 antigen detection begins to decline and anti-dengue IgM antibody rises, making serology (IgM/IgG ELISA) more appropriate from day 5 onwards. Serotyping by RT-PCR is epidemiologically important for surveillance of circulating serotypes.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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